Metal treating compositions and processes



United States Patent 3,314,811 METAL TREATING COMPOSITIONS AND PROCESSESAbraham J. Mitchell, Stratford, and Paul R. Jarvi, Orange,

This invention relates to the art of blackening aluminum surfaces orsurfaces of aluminum alloy metals in which aluminum is the majoringredient, and to the novel aluminum blackening compositions foraccomplishing this result.

Aluminum and its alloys are of ever-increasing importance for thefabrication of countless items because of the lightness, workability,strength and other inherent properties of these metals.

Aluminum has a bright metallic surface which is not receptive to orretentive of applied colored coatings or protective coatings of oil orwax and which becomes whitish in color upon prolonged exposure to theatmosphere due to the oxidation of the aluminum to form a white aluminumoxide surface coating.

It is well known to electrolytically plate or anodize aluminum to formthereon a non-corrosive non-oxidizable coating which protects theunderlying aluminum against contact with the atmosphere and which inturn may be dyed any desired color. While such anodizing processes areeffective in accomplishing the desired results, they are neverthelessslow, costly and unavailable to those who do not possess electroplatingequipment.

It is an object of the present invention to provide an aluminumblackening composition which may be applied at room temperatures or anyhigher or more convenient temperatures by conventional immersiontechniques and in the absence of applied current to form on the aluminumsurface black coatings which are strongly bonded and which resistchalking or flaking off.

It is another object of this invention to provide a rapid andinexpensive process for applying coatings to aluminum which arereceptive to and retentive of protective wax or oil coatings without thedisadvantages of the electrolytic anodizing process.

These and other objects and advantages are accomplished by the presentinvention as Will be clear to those skilled in the art in the light ofthe following description.

The essence of the present invention resides in the discovery of anaqueous solution of certain water-soluble compounds which cooperate todeposit black or off-black coatings on aluminum surfaces which areimmersed therein for relatively short periods of time and at relativelylow temperatures.

The aqueous blackening compositions of the present invention are acidicaqueous solutions which contain a mixture of compounds which react withthe aluminum surface to render it receptive to the blackening compound,and a mixture of blackening compounds selected from the group consistingof molybdic acid and salts thereof and sulfur-bearing compound-s.

It appears that this preferred composition fulfills a twofold etfect inwhich the aluminum surface is both etched and coated with a metalliccoating, the etching step rendering the surface receptive to the depositof black molybdic oxide and the metallic coating step forming a Cit witha sulfur-bearing compound reaction product which appears coating whichis reactive to form the black or gray to be a sulfide.

The first blackening combination in the mixture comprises awater-soluble chlorine compound which ionizes to form chloride ionswhich function to etch or otherwise roughen the aluminum surface, andmolybdic acid or the water-soluble salts thereof which function todeposit black molybdic oxide on the roughened aluminum surface. Thiscombination of materials when used in an aqueous solution having a pH ofabout 6.5 or less has. been found to form black coatings which arefirmly bonded to aluminum.

Suitable chlorine compounds include the alkali metal chlorides such assodium chloride and potassium chloride, ammonium chloride, hydrochloricacid and the like watersoluble ionizable chlorides.

Suitable molybdic oxide liberating compounds are molybdic acid orhydrogen molybdate and the water-soluble salt-s thereof such as thealkali metal molybdates including sodium molybate and potassiummolybdate, ammonium molybdate and the like.

The second blackening combination of the mixture encompassed by thepresent invention comprises the watersoluble salt of a metal belowaluminum in the electromotive series, and a watersoluble sulfur-bearingcompound.

The metal salt ionizes in solution to form metal cations which depositin an acid medium on the aluminum surface to form a surface film whichappears to be receptive to or reactive to form black metal sulfurcompounds or complexes.

Metal salts found suitable for treating the aluminum surface to renderit receptive to black metal sulfide deposits include the salts asbroadly defined and more specifically includes the sulfates,dichromates, nitrates, chlorides, acetates and other watensol-uble saltsof metals such as nickel, chromium, cob-alt, antimony, bismuth, arsenicand any of the other metals which have a lower electrode potential thanaluminum and are therefore below aluminum in the elect-rom-otive seriesand which are therefore replaced from their salts by aluminum.

Water-soluble sulfur-bearing compounds found suitable for the formationof black metal sulfur react-ion products in an acid medium includesulfides, thiocyanates, thiosulfates, thioureas,Z-mercaptobenzothiazole, benzothiazyl disulfide, Z-me-rcaptoimidazolineand the like, and including most preferably sodium thiocyanate, sodiumsulfide, sodium hyposulfate and the like.

According to the present invention, an aqueous blackening composition isformulated so as to include both blackening compositions heretofore setout. It has been found that when a single blackening composition is soformulated it provides a bath which blackens aluminum more deeply andmore evenly and smoothly than is possible using either of the othercompositions alone. From these standpoints the behavior of thecombination aqueous blackening composition is synergistic.

This preferred blackening composition include at least two chemicalswhich affect the aluminum surface in different manners to render itreceptive to the deposit of blacking agents. These chemicals are thechlorides which tend to etch or otherwise attack the aluminum surface,and the salts of metals below aluminum in the electromotive series whichdisplace the aluminum to form a metallic film which is reactive to formblack metal sulfur compounds or complexes on the surface thereof.

The composition also includes at least two blackening compounds, one ofwhich deposits black molybdic oxide on the aluminum and the other ofwhich contains sulfur and is reactive with the deposited metal film toform the black metal sulfur compounds or complexes.

The blackening compositions contain the following ingredients in thefollowing proportions:

Range in Percent by Weight Ingredient Broad Preferred Molybdic acid orsalt 2 to 25 3 to 10 Metal salt 3 to 40 3 to 20 Water-soluble chloride.40 to 80 50 to G Sulfur-bearing compound 0. 5 to 20 1 to 5 Acid 5 to 60to 30 Fluorine-bearing compoun 0 to 5 to 15 The following example isillustrative of a preferred composition for However the specificingredients and proportions are set forth as illustrative and should notbe considered limitative, possible variations being clear to thoseskilled in the art in the light of the disclosure set out hereinbeforein connection with the previous formulation.

These ingredients are dissolved in water in a concentration ranging fromabout 1 ounce per gallon up to about 3 or more pounds per gallondepending upon the results desired. In most cases it is preferred to usea concentration in the area of from 2 to 10 ounces per gallon and mostpreferably about 6 ounces per gallon of water. 1

The fluoride ingredient is found to cooperate with the chloride inetching the aluminum surface. Similar results are obtained through theuse of soluble fluoborates, fluorides and bifiuorides. If hydrofluoricacid is used for this purpose it may also function to replace some ofthe acidifying agent such as the sodium bisulfate.

A blackening bath prepared in this manner is preferably heated to atemperature of between about 120 F. and 180 F. and most preferablybetween 150 F. and 160 F. for use, although it has been found effectivein accomplishing the desired result at temperatures as low as about 50F. and as high as its boiling temperature which is somewhat in excess of212 F. Low temperatures require longer immersion periods while hightemperatures result in deposition too rapidly and quite unevenly.

The aluminum pieces are immersed in the blackening composition for aperiod of from 1 to minutes depending upon the specific acidity of thesolution and its temperature. Generally an immersion time of from 10 to15 minutes is sufficient to form a dark black deposit which is smoothand even and which is firmly anchored to the aluminum surface. Thealuminum is removed from the composition and washed or rinsed.

In cases where it is desired to further treat the aluminum to provide itwith an oxidation-resisting, corrosionresistant coating, the blackenedaluminum pieces are immersed in any conventional wax, oil or resincomposition to deposit over the blackened surface a protective coatingor shield. This is not practical with untreated aluminum since thesurface has no afiinity for an oil, wax or resin coating and attempts toapply and retain such coatings thereto are unsuccessful. However thepresent blackened deposits on aluminum are found to provide a useaccording to the present invention.

perfect receptive surface for such protective coatings and appear tobecome integrated therewith to form a solid bond.

As protective coatings it is preferred to use thin solutions of oils andwaxes which penetrate the blackened deposit on the aluminum and displaceany water remaining therein as a residue of the aqueous blackeningcomposition. When the pieces are withdrawn from the protective coatingsolutions the coatings dry quite rapidly in the form of very thinprotective films or shields.

The phrase blackening composition as used herein and in the appendedclaims is intended to include compositions useful for applying jet blackor off-black coatings including those in which the deposit is ratherlight or thin and which appear to have a gray color due partly to theshow-through of the underlying aluminum.

While the compositions of the present invention have been discussedprimarily in connection with their use in the blackening of aluminum andaluminum alloy metals, it should be understood that the presentcompositions are also useful for the blackening of other metals such asiron, stainless steel, brass, copper, Zinc, titanium, magnesium and thelike. The present compositions are particularly adapted for thecoloration of aluminum in view of the many problems encountered inconnection with the coloration of aluminum and the provision of aluminumwith a coating receptive to protective outer coatings of oil or wax.

Variations and modifications may be made within the scope of the claimsand portions of the improvements may be used without others.

We claim:

1. The method of blackening aluminum which c0m prises the steps ofpreparing a blackening com-position by dissolving in water from about 1ounce to about 3 pounds per gallon of a mixture of compounds which arereactive with aluminum to render it receptive to the deposit ofblackening compounds com-prising. up to by weight of a water-ionizablechloride and from 3% to 40% by weight of water-soluble salt of a metalfalling below aluminum in the electromotive series, and a mixture ofblackening compounds comprising from 0.5% to 20% by weight ofwater-soluble sulfur-bearing compound capable of forming a blackmetal-sulfur reaction product upon reaction with the said metal fallingbelow aluminum in the electromotive series and from 2% to 25% by weightof water-soluble molybdate, maintaining the pH of the solution belowabout 6.5, maintaining the temperature of the solution within the rangeof from about 50 F. to about 212 F., immersing the aluminum into theblackening composition for a period of from 1 to 30 minutes, andremoving the blackened aluminum.

2. The method according to claim 1 in which the temperature of thesolution is maintained within the range of from about F. to about 180 F.

3. The method according to claim 1 in which the water-ionizable chlorideis selected from the group consisting of alkali metal chlorides,ammonium chloride and hydrogen chloride.

4. The method according to claim 1 in which the sulfur-bearing compoundis selected from the group consisting of a sulfide, thiosulfate,thiocyanate, thiourea, 2-mercaptobenzothiazole, benzothiazyl disulfi-deand Z-mercaptoimidazoline.

5. A blackening composition useful for the blackening of aluminumsurfaces when dissolved in an aqueous solution in an amount ranging fromabout 1 ounce to about 3 pounds per gallon, said composition comprisinga mixture of compounds which are reactive with aluminum to render itreceptive to the deposit of blackening compounds and which comprise upto about 80% by weight of a water ionizable chloride and from 3% to 40%by weight of water-soluble salt of a metal falling below aluminum in theelectromotive series, and a mixture of blackening compounds comprisingfrom 0.5% to 20% by weight of water-soluble sulfur-bearing compoundcapable of forming a black metal-sulfur reaction product upon reactionwith the said metal falling below aluminum in the electromotive seriesand from 2% to 25% by weight of watersoluble moly bdate.

6. A blackening composition according to claim 1 in which thewatenionizable chloride is selected from the group consisting of alkalimetal chlorides, ammonium chloride and hydrogen chloride.

7. A blackening composition according to claim 1 in which thesulfur-bearing compound is selected from the group consisting of asulfide, thiosulfate, thiocyanate, thiourea, Z-mercaptobenzothiazole,benzothiazyl disulfide and Z-mercaptoimidazoline.

References Cited by the Examiner UNITED STATES PATENTS Vande Bunte252-79.2 Singler 1061 XR Jendzynski 1061 Mason 1061 XR Baig et al 106-lXR Bellinger 25279.3 XR

ALEXANDER H. BRODMERKEL, Primary Examiner. J. B. EVANS, AssistantExaminer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,314,811 April 18, 1967 Abraham J Mitchell et a1 It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below.

Column 4, lines 0,43,46,74 and 75, before "water-soluble,

each occurrence insert a column 5 line 3 before "water" insert a lines 5and 9 for the claim reference numeral "1", each occurrence read 5 Signedand sealed this 2nd day of January 1968 (SEAL) Attest:

EDWARD J. BRENNEF Commissioner of Patents Edward M. Fletcher, J r.

Attesting Officer

1. THE METHOD OF BLACKENING ALUMINUM WHICH COMPRISES THE STEPS OFPREPARING A BLACKENING COMPOSITION BY DISSOLVING IN WATER FROM ABOUT 1OUNCE TO ABOUT 3 POUNDS PER GALLON OF A MIXTURE OF COMPOUNDS WHICH AREREACTIVE WITH ALUMINUM TO RENDER IT RECEPTIVE TO THE DEPOSIT OFBLACKENING COMPOUNDS COMPRISING UP TO 80% BY WEIGHT OF A WATER-IONIZABLECHLORIDE AND FROM 3% TO 40% BY WEIGHT OF WATER-SOLUBLE SALT OF A METALFALLING BELOW ALUMINUM IN THE ELECTROMOTIVE SERIES, AND A MIXTURE OFBLACKENING COMPOUNDS COMPRISING FROM 0.5% TO 20% BY WEIGHT OFWATER-SOLUBLE SULFUR-BEARING COMPOUND CAPABLE OF FORMING A BLACKMETAL-SULFUR REACTION PRODUCT UPON REACTION WITH THE SAID METAL FALLINGBELOW ALUMINUM IN THE ELECTROMOTIVE SERIES AND FROM 2% TO 25% BY WEIGHTOF WATER-SOLUBLE MOLYBDATE, MAINTAINING THE PH OF THE SOLUTION BELOWABOUT 6.5, MAINTAINING THE TEMPERATURE OF THE SOLUTION WITHIN THE RANGEOF FROM ABOUT 50*F. TO ABOUT 212*F., IMMERSING THE ALUMINUM INTO THEBLACKENING COMPOSITION FOR A PERIOD OF FROM 1 TO 30 MINUTES, ANDREMOVING THE BLACKENED ALUMINUM.
 5. A BLACKENING COMPOSITION USEFUL FORTHE BLACKENING OF ALUMINUM SURFACES WHEN DISSOLVED IN AN AQUEOUSSOLUTION IN AN AMOUNT RANGING FROM ABOUT 1 OUNCE TO ABOUT 3 POUNDS PERGALLON, SAID COMPOSITION COMPRISING A MIXTURE OF COMPOUNDS WHICH AREREACTIVE WITH ALUMINUM TO RENDER IT RECEPTIVE TO THE DEPOSIT OFBLACKENING COMPOUNDS AND WHICH COMPRISE UP TO ABOUT 80% BY WEIGHT OF AWATER IONIZABLE CHLORIDE AND FROM 3% TO 40% BY WEIGHT OF WATER-SOLUBLESALT OF A METAL FALLING BELOW ALUMINUM IN THE ELECTROMOTIVE SERIES, ANDA MIXTURE OF BLACKENING COMPOUNDS COMPRISING FROM 0.5% TO 20% BY WEIGHTOF WATER-SOLUBLE SULFUR-BEARING COMPOUND CAPABLE OF FORMING A BLACKMETAL-SULFUR REACTION PRODUCT UPON REACTION WITH THE SAID METAL FALLINGBELOW ALUMINUM IN THE ELECTROMOTIVE SERIES AND FROM 2% TO 25% BY WEIGHTOF WATERSOLUBLE MOLYBDATE.